Light-flash-producing system



Aug 16 194% H. E. EDGERTON 24%3 LIGHT-FLASH-- PRODUCING SYS TEM Filed Dec. 50, 1959 2 Sheets-Sheet 1 Aug 19490 H. EDGERTON 2,478,9fl

I LIGHT-FLASH-2RODUCING SYSTEM I Filed Dec. 30, 1939 2 Sheets-Sheet 2 'a d!i mve.d; sys;temforpr dtming stmmlel athe-s id v pp i at qnnth rei cdifile ede 119W intense substantially uniform electric-energtg: li h -fla h sam ane tzae erx ma l-amount r Q-.- 1 :ey l w esxg iron: s cenflensee uiet y. iab e. ,A .eqqu cate x;'-at!., i afr e uenqm eht, ee usa qmw o l m xet mi imn e andemsgfidz nccnetmct tr iiL-W m'mPQF b1 8.1M self we we t W M M M1 2:- .7 W2 i i fi @W' Q 551 witho t-mo fiexeee eit rteet een ,ie uefiiffih mecca? Wii 'j an ntacto efliegtiye ,0 ofcontrol-grid or'startirigelectrpde "including eeire a lemaeaeqe ii v sc w-92m re ee Though it is explained, int n that. e u t w i ien/Mime lisflaslws'is deter ined by the amount of energ ii hegcen ti attire in densevrfandlba m tc ndi i nsha is 511.03% Goff? claime d'inthe pfes'iit appueatjieii; I 7 7 The.- invention; will nowbe .deseribedliixi ckinnecticn. with. the accompanying. ,drawingg m which fighl diagi'am.rn"",at1c aw; dfi-icirejiits and;apparatus,arrangefiaiidicbnstructedfacdra ing to dii'eefiibodimen't 16f .vthejin'v'entie *.;.E igs, 2,-and,s, alleimddificafii hs. ofgtneisanialiahwgs. 4; 5 am; 6."illustiatejjmodifiemstrobbscfipe figh pmce circuitsemhcdyinaaniemfiifit'm t oci Q iergingtm condensers. As, described in the saidapp'lication, alluinin escent vapor electric gaseous-discharge flash lamp or..fiash tube 2 or I01 provided with twolim ternal main or, principal electrodes 4 anditinna glass-tube, envelope. Other apparatus-'than-the illustrated lamp 2 may also he used in accordance with the present invention. The principal. elc: trodes 4 and, 6 define aprincipalcurrenhpath for theilamp 2; The lamp 2 is vdescribedinuthe said applicatiQn. as of the .loweimpedancegniere curyarc gaseous-conductor type, a ,the ixii brnal electrode 4 being shown as, in theformpf ,atliquid t pool of mercury, .us ed for acathode, ,andjthein: an ingiuctg nces no shmgn lg ternal electrod 6 servingnasrtheqanode.oi.pl ate, be pmvided as partaogt thicqntgentional so as The remarksthroughout,lthisflspecificati lnjcom of di're'ctcurnenta' i 1 j cerningmercuryearct'ubes m fimjsi' e i! ima welllltofltubes orjlamp'slfill'ed .lwithl-ofl eriasg's, 263s normally charged with energy gredgwitl'i'orwitho'ut'mercury'vap i'. tw eeqeeaene weee emeeeen to the full potential of that source. This charging may be enected by connecting the flash condenser 26 to the source or direct current in any desired manner, as by means of the wire conductors 8 and I0. The flash condenser 26 is shown connected to the source of direct-current potential in parallel with the principal electrodes 4 and 6. The electrodes 4 and 6 are therefore connected in series with the two terminals of the hash-condenser source of energy at the same time that energy is thus supplied to the flash condenser 2c Irom the source of direct current. The usual voltage to which the condenser becomes thus charged is from 200 to 2,000 volts.

The charging circuit for the condenser 26 is shown extending from the positive terminal of the battery I02, or from the rectifier 20, by way or the conductor I0, to the corresponding positive terminal or the condenser 26; and from the negative terminal 02 the battery I02, by way of the conductor 8, to the negative terminal of the condenser 26; A current-limiting charging impedanc 35 may be series-connected in the charging circuit or the condenser 26, between the condenser 26 and its charging source of direct current, either in the wire conductor I0, as shown in Figs. 4 and 5, or the wire conductor 8, as 11- lustrated in Figs. 1, 2 and 3.

' Because of the dielectric properties of the normally deionized mercury vapor or other gas in the space of the lamp 2, between the cathode 4 and the anode 6, the battery I02 or other directcurrent source will before each flash charge the flash condenser 26 through the impedance 35 so that the anode 6 is positive, without any of the energy of th battery I02 traversing that space. A difference of potential of unvarying polarity will therefore be established between the oathode. 4 and the anode 6 during the charging of the condenser 26.

After becoming thus charged, the condenser 26, as will presently be more fully explained, may be discharged through the gaseous medium of the lamp 2, between the anode 6 and the cathode 4, in the discharge circuit of the lamp 2. The lamp 2 will be recognized by persons skilled in the art as of the type in which a positive-column discharge may pass between the anode electrode 6 and the cathode electrode 4. The discharge current thus obtained from the flash-condenser source of energy results in the production of an electric-energy light flash through the lamp 2. The major portion of the energy supplied from the flash condenser source of energy in the seriescircuit connection between the terminals of the flash condenser 26 and the principal electrodes 4 and 6 is consumed in the positive-column discharge, with the result that the light flash is of high illumination intensity and short duration.

The condenser-discharge circuit is shown extending from the positive terminal of the condenser 26, by way of the conductor I0, directly to the anode electrode 6; and from the negative terminal of the condenser 26, by way of the conductor 8, directly to the cathode electrode 4. The cathode 4 and the anode 6 of the lamp 2 are thus series-connected by the conductors 8 and I to the condenser 26 in this condenser-discharge circuit directly across the condenser 26. The connections are such as to enable the condenser 26 to discharg with relative rapidity through the lamp 2 between the anode electrode 6 and the cathode electrode 4 when the lamp 2 becomes conductive. v

The impedance 35 should be designed sutflciently large so that, after the discharge of the condenser 26 between the cathode 4 and the anooe 6, further current flow between them will be prevented until after the gaseous space in the lamp 2 between the electrodes 4 and 6 shall have again become deionized. The condenser 26 is therefore normally charged'to a voltage of unvarying polarity and of magnitud insufiicient to efiect a discharge of the condenser through the lamp between the electrodes 4 and 6 when the lamp is non-conductive, though sufficient to effect a discharge of the condenser 26 through the lamp between the electrodes 4 and 6 when the lamp is conductive. The impedance 35 should, however, be small enough to permit of the re-establishment of sufiicient difference of potential between the cathode 4 and the anode 6 to enable recharging of the condenser 26 with energy from the direct-current source in time for the next flash. These ends may be attained by rendering the impedance 35 suitably reactive, as by constituting it of a wire conductor comprising a combination of resistance and inductance. The size and characteristics of the impedance 35 should be determined by the characteristics of the flash lamp 2 or other apparatus in connection with which it is used and the desired time interval between th condenser discharges. This feature, as stated in the said application, is claimed in a copending divisional application, Serial No. 688,406, filed August 5, 1946.

As is stated in the said application, Serial No. 685,501, the quantity of stroboscopic light is determined by the amount of energy in the condenser 26 and by circuit conditions. The capacity of the condenser 26 is increased until there is suflicient average light for th particular frequency of flashing and the extraneous illumination. Slow speeds require a larger amount of light per flash than fast speeds to give the same average illumination.

Five possible methods of varying the amount of light are:

1. Changing the capacity, as by varying the capacity 26. The amount of light for each flash is almost proportional to the capacity and the square of the voltage.

2. Changing the voltage, as indicated by the tapped input supply battery or power supply I02, in Fig. 2. There are many well-known methods of varying the input voltage, either manually or automatically, to suit requirements.

3. Changing the value of a series resistor II in the lamp discharge circuit, as indicated in Fig. 1. The light decreases as the resistance increases, since more of the energy is lost in the resistor.

4. Changing the value of an inductance I2 in series with the lamp, in the condenser-discharge circuit, as indicated in Fig. 2. The light is decreased as the inductance is increased. This variable inductance may be of the variometer type, consisting of two coils movable with respect to each other.

5. Changing the secondary impedance 6| of a transformer 60 that is connected in series with the discharge current, as illustrated in Fig. 3. the secondary impedance 6| of this transformer may be inductive, capacitive, resistive, or any combination of these. It may further consist of vacuum or gas-filled tub-es, without moving parts, according to methods well known in the art, for automatically controlling the amount of light, in accordance with any desired. requirements.

' As is also explained-in the; said; .-:applicatiop;, S rial No. 68.5. 15; h :d1scharee f Q:" 4$h? condenser 26 through the condenser -discharge; circuit above described is initiated lay-energizing the normally unenergizedstarting; electrode. N10,, under the control of a. trip circuit. The trip circuit is 'showncomprising a. second normally non-conductive or ineffective gaseous-discharge trigger-tube device MU, a small'auxiliary oap'ac itor or condenser 28, a second suitable directe current source of energy; such asa second battery lEil, or some rectified source of alternatingenergy for charging the small auxiliarycon denser 28 at a predetermined rate, and a nor-- mally' ineffective triggering or: trip flash transformer St. For definiteness, the larger; flash condenser 23 may be referred'to as-agfirst cone denser, and the small auxiliary condenser-28*as a, second condenser.

A further such trip circuit-isshownin Fig fg comprising a second such tube- I40 (not shown),

a second such capacitor-2B (not shown), and a second such transformer 3911. As these trip-circults are alike, only one of them is described in the specification of the said application, Serial No. 685,501.

The gaseous-discharge device l wmay be constituted of a mercury-vapor thyratron, a gasfilled hot-cathode thermionic tube or a grid-controlled cold-cathode arc-discharge tube or any other suitable discharge device. The, transform-- er 3i) may be of the high-ratio, step-up or any other; desired type, with a relatively low-impedance primary winding- 35, and a secondary winding 25, shown connected between the cathodel and the external electrode Hit; ,Thebefore?v mentioned starting-currentpath of the lamp 2, extending from the starting electrode I98 to, the cathode 4, includes the'inductanceeof-"the'sec! ondary winding 29. tain other elements also; for example, in Fig; 1', the two impedances 3! and 33, and, in Fig. 2, the two impedances 3i and I33, all shown re sistive, and connected into circuit with the source of potential ldl.

The trip circuit may perform its function of initiating the discharge of the condenser- 26 through its discharging circuit by converting thedirect current of the second source of potential, such as the battery Nil, into very sudden voltage pulses in the primary winding 35 of; the flashtransformer 36. These, as will be described more fully presently, will be manifested as alternatingcurrent pulses in the secondary winding 29.

the tube M0, like the lamp 2, may be a rectifier of the arc-like discharge type,-conductive in one direction only, it serves also as an electric check valve. It is shown provided with at least three electrodes. Two of theseare main or principal electrodes, namely, an anode or plate 52 and cathode 8. The third is a control-grid electrode 55. These three electrodes correspond tothe anode 6, the cathode 4 and the control electrode liiii, respectively, of the flash lamp 2. The tube Hi9, like the tube 2, may be of the type having an abrupt characteristic. To. energize the tube Hit, a maximum predeterminedpoten, tial maybe impressed across it, betweenits two main or principal electrodes,,without appreciable current flow between these electrodesg andasubstantially constant potential difference may' be impressed between the control electrode and {one of the principal electrodes; Thegas pressure;. ot h tube... iil. is. suchthat .1 l Q-Q L W L LQQHQM- The trip. circuit 1. may contery lfll, in series with the resistor 3i.

;- circuit. These willfirst be described in connec tion with-the trip circuit of Figs. 1 and 2.

The-output circuit of the trip circuit of Figs. ;1*- and 2, or of the thyratron I49,- may be traced, from-thecathode 48, through the primary wind-.

.- ing- 36 of the flash transformer and the small;

second condenser 28, to the anode 52. This out-- put circuitiof-the: trip circuit of Figs. 1 and-2'; is connected to the lamp 2, since it includesthe; inductance ofthe primary winding 36. of, the flash transformer 36, thesecondary Winding 29- of which has before been-described as connected; inthe starting-current path of this lampZ.

It has been. stated that the small second condenser 28 in this output circuit of the trip air-- uit is charged fromthe battery Efil. The inn-- pedance I33 of Fig. 2, like-the impedance 33- of Fig. l, is shown shunted across, or connected; in parallel with, the small condenser 28. Each of'theseimpedances Stand Q33 is also connected in' parallel with the output circuit of the trip: circuit; comprising not only the condenser 28, but also the cathode 48 and the anode 52 of the tube ME! and the primary winding 36 of the flash; transformer 30, connected in series. The posi tive terminal of the battery Hil is connected to one terminal of the small, second condenserZB and one terminal of the resistor 33 or 533",dlf1d1 thenegative terminal of the battery Nil is-connectedtothe other terminal of the small condenser 28 and the other terminal of the resistor 33 or I33, through the resistor 3!. Power is thus obtained :for the thyratron ltd and for charging the small second condenser 28 in the output circuit of" the trip circuit from the bat- The tripcircuit output circuit of Figs. 1 and 2, comprising the primary winding 36, the tube Md and the small second condenser 28, in series, may therefore be regarded as obtaining its energy from this small condenser 28, after becoming charged.

from the battery NH. The battery lfil may, however, also be regarded as included within the output circuit of the trip circuit of Figs. l and 2: The resistor 3! may perform a function similar to that of the impedance in the charging cir cuit of the condenser 26. The resistanceiofthe. resistor 3| may initially beso adjusted as to pre vent self operation of the trip circuit when the small second condenser 28 becomes charged. 7

The controi input circuit of the trip circuit of Figsg'l and 2 is the same as the input or grid circuit of the thyratron or other gaseous-dis-v charge tube Mll. In Fig. 2; this control input circuit may be traced from p the cathode 48, through theprimary winding 3%, the portion of the impedance 3| to the left of a tap IEI, and thesecondary winding of a trip or grid transformer 64, the function-of which will be explained presently, and through an impedance, shown as aresistor I42, to the control-grid electrodeill. Theioorresponding control input circuit of Figl contains aportion of the resistor 33, instead of the; resistor 31, as in the-system of Fig. 2, and i sdo s n tl con ai ;.mes nd n n lass the trip or grid transformer 64. These difierences will be discussed more fully presently.

The resistor I33 of Fig. 2 only is a bleeder resister. The connection of this bleeder resistor I33 to the battery Il before described is such as to allow a small current to flow in the resistor 3|. A voltage becomes thereby established across the resistor 3! for impressing upon the control grid 50 of the thyratron I40 in these control input circuits a normal bias suitably negative with respect to the thyratron cathode 48. The control grid 50 is connected to the negative end of the resistor 3|. As will hereinafter appear, advantage is taken of this normally negative voltage bias provided by the resistor 3! upon the control grid 50 to render the normall ineffective tube I40 efiective at desired instants of time.

The resistance I33 is necessary to prevent the self-operation of the thyratron I40 when the condenser 28 becomes fully charged. The said resistance I33 (illustrated in Fig. 2 only) is made to have a large value, or is disconnected, when self-oscillations of the thyratron are desired as hereinafter more fully described.

The discharging circuit for the small condenser 28, in the trip circuits of Figs. 1 and 2, may therefore be traced from one terminal of the condenser 28, through the tube I40 and the primary winding 36, in series, to the other terminal of the small condenser 28. As soon as the normally non-conductive gaseous-discharge trigger tube I40 of the trip circuit is rendered conductive, therefore, the energy of the small condenser 28 is discharged through both the thyratron I40 and the primary winding 38, in series.

The conversion effected by the trip circuit of the direct current of the battery it" into alternating-current pulses may be efiected by this discharge of the small condenser 28 through the primary winding 33 of the flash transformer 30.

The condensers 23 and 28, however, may be charged through the impedance 35 from a common source of potential, as shown in Fig. 6.

The output circuit of the trip circuit or of the tube I40 of Fig. 3 may be traced from the oathode 48, through the small second condenser 28 and an impedance 33, shown as a resistor, connected in parallel, and through the primary winding 36, to the negative terminal of the battery WI. The output circuit is completed from the positive terminal of the battery IOI, through a variable impedance l9, shown as a resistor, to the anode 52. As in the case of the trip circuits of Figs. 1 and 2, therefore, the battery IOI is included in the output circuit of the trip circuit of Fig. 3 also. An impedance 3|, shown as a resistor, is connected in parallel between the cathode 48 and the anode 52. A by-pass condenser, not shown, is usually shunted across the battery IOI to by-pass the current surges that charge the condenser 28. This by-pass condenser may serve as the source of energy for the output circuit of the trip circuit of Fig. 3.

The inductance of the primary winding 33 in the starting-current path of the tube 2 is therefore connected in the output circuit of each of the trip circuits of Figs. 1, 2 and 3, between the cathode 48 and the plate or anode 52, in series with the small second condenser 28. The output circuit of each of the trip circuits of Figs. 1 and 2, however, as before described, is connected in shunt to the second battery Ifii. In the trip circuit of Fig. 3, on the other hand, the small d second condenser 28, the primary winding 36 and the tube I40 are connected in series with the battery NH.

The control input circuit of the trip circuit of Fig. 3, or the input or grid circuit of its thyrag tron I40, may be traced from the cathode 48, through the small second condenser 28 and the impedance 33, in parallel, and from a tap I49 of the impedance 33, by way of an impedance, shown as a resistor I42, to the control-grid electrode 50. The negative bias upon the control grid 50 through this resistor is developed across the resistor 33 from the battery IOI in the circuit extending from the positive terminal of this battery IIJI, through the resistors I9, 3I and 33, and through the primary winding 36, to the negative terminal of the battery Illl.

Because of the normally negative potential bias impressed on the control grid 50 in the control input circuit of the trip circuit of each of Figs. 1, 2 and 3, therefore, the output circuit is maintained normally open, to render the thyratron I40 normally non-conductive.

The control-grid electrode 50 may be caused to determine the exact instant when the normally non-conductive thyratron I40 shall become conductive. This control by the grid electrode 50 may be exercised by suitably modifying the potential difference between the negatively biased control grid 50 and one of the principal or main electrodes, as the cathode 48, to a predetermined critical value in order to energize the normally unenergized control input circuit of the trip circuit. This may be efiected by subjecting the .control grid 50 to a suitable stimulus, as will be described hereinafter. The normally open output circuit of each of the trip circuits of Figs. 1, 2 and 3 thereupon becomes closed or completed from the anode 52 to the cathode 48, in series with the low-impedance primary winding 36 and the small second condenser 28.

Referring to the trip circuits of Figs. 1, 2 and 3, the small second condenser 28 having meantime become charged, the energy thus stored in the condenser 28 becomes suddenly discharged through this output circuit of the trip circuit, between the anode 52 and the cathode 43. A sharp violent high-potential single electrical transient impulse becomes thus quickly, accurately and reliably impressed very suddenly, for a brief interval of time, upon the primary winding 36 of the thyratron trip circuit, at the exact instant desired, accompanied by a sudden surge of current therethrough.

The resulting high-potential trip surge across the terminals of the secondary winding 29 becomes conveyed, accurately and reliably, to impress a high-potential stimulus between the starting electrode Hit and the cathode 4 of the tube 2. In response to this sudden energization of the starting electrode I00, a triggering surge or pulse of current becomes thereupon suddenly initiated in the starting-current path between the control electrode I00 and the cathode electrode 4, resulting in the formation of a bright cathode spot of light on the surface of the mercury-pool cathode 4 at the junction between the mercury and the inner wall of the glass tube 2. A source of electrons becomes thereupon created upon the mercury cathode 4, in the vicinity of the cathode spot. These electrons ionize the normally un-ionized gas in the normally non-conductive lamp 2, to render it conductive. The flash condenser 26 having previously become charged to a suitable potential, it thereupon, at

the exact instant determined by the potential impulse upon the control grid 50, discharges quickly and violently to initiate current flow :through the principal current path, including the gaseous medium of the lamp 2, between the cathode electrode i and the anode electrode 6. This violent electrical transient surge of current through the gaseous medium of the lamp 2 between the cathode 4 and the 'anodeli, thus produced in response to the potential stimulus impressed upon the thyratron grid 50, initiates, as before stated, a very brilliant intense quick sharp clear flash of light'of high illumination intensity. At the instant of discharge, the current surge through the lamp 2 is very great. It may be over onethousand-amperes.

Because of the low impedance of the mercury lamp 2, the duration of the flash discharge is short, of the order of microseconds, as determined by the size of the capacity 26, the dimensions of the lamp 2, its volt-ampere character istics, its temperature, the impedance of the con ductors 8 and I 9 connecting the condenser 26 and the lamp 2, and other factors. The inductance of the conductors 8 and It is useful in extinguishing the arc, as it tends to make the discharge current oscillatory. Under some conditions, the duration of the flash is less than even one microsecond.

The are through the lamp 2 'isnot maintained,

but is promptly extinguished, because of the current-limiting action of the impedance 35. At the end of a predetermined interval of time, therefore, the current flow in the principal-current path becomes discontinued. The condenser 25 becomes thereupon again charged, in preparation for the next discharge.

The tube 140 therefore serves as a relay for accurately timing the starting of the mercuryarc tube 2. microamperes of current "in the control input or grid circuit of the thyratron or other gaseousdischarge tube Me, to stimulate the grid 50, in the manner more fully described hereinaftenwill effect the discharge of the small second con-1;

denser 28 through the output circuit, including the primary winding 36, at just the instantof time desired.

The timing voltage impulses in the control input circuit of the trip "circuit for stimulating the: control grid 56, in order to raise it to the predetermined critical value necessary to trip the thyratron MiL-so as to render it conductive, may be obtained through the medium of an external signal. *If the signal is reproduced at a 'predetermined rate repetitively, many times a secnd, at selected intervals determined by the predetermined rate, the res-ulting'periodically pro- I ducted-flashes may be used, for-example, for stroboscopic purposes; for the apparent speed of a moving object becomes thereby so effectively reused, and the moving object moves so inappreciable a distance-during the period 'of the "flash, that it appears to be"stopped. Single signals, however, may also be used, as in flash photography. a

, In the trip'circuit of Fig. '2, the external "signal for rendering the tube 2 conductive is produced in the control input circuit with the aid of the trip or grid transformer 54 from an oscillator 62. The transformer -64 may be of the type that will yield a peaked secondary voltage. In response to the oscillation pulses of the oscillator 52, impulse charges become suddenly impressed A timing impulse of only 'a -few;:

' in the 'output circuit. 7

5,0 in order suitab'ly tomodify'the potential there- 'of. It is in this manner that the potential of the control grid 50 intermittently becomes sufliciently critical with respect to the potential of the cathode 48 of thethyratron I40 to energize the normally unenergized control input circuit of the trip circuit, in order to render the thyratron 1-40 conductive.

. Referring again'to Fig. 2; the'small second condenser '28 discharges suddenly through the output circuit of the trip circuit in response'to each 'of'these impulses in order to establish suddenly the before-mentioned violent high-potential single electrical transient pulse, in this 'output circuit. A high-potential gradient becomes thus established in the output circuit in response to each such discharge of .the small second condenser 28.

Corresponding energizing pulses are thereupon produced intermittently in the transformer 30 to effect sudden transient energiza-ticns of the normally unenergized starting electrode H10, intermittently to render the lamp 2 suddenly con- -.du'ctive at times determined by the dischargesof "the small second condenser 28. At each such discharge of the small condenser '28, the normally 'inefiective transformer 30 becomes thus suddenly effective *to' subject the starting electrode 190 of the tube 2 to a relatively high po- 'tential. This, as beforestated, renders the "tube '2 suddenly COIldLlCtiVdill order that a current impulse may-be obtained through the gaseous medium of the tube -2, by the discharge of the condenser 26, between the cathode 4 and the anode 6; to produce the flash. This result "is effected *without the aidiof any switches in the high-voltage circuit, =merely-by having the osciliator 6-2 supply periodically the .signal charges tothe grid 50.

The duration or each such sudden discharge of the condenser 2-8 through the output circuit constituted of the" small second condenser 28 produced by't-he before described'impulse upon the control grid -50 is short compared to the times b'etweensuccessive discharges of the small second condenser 28. This is because the control grid 50 is normally maintained at a potential such as to render the "thyratron I40 -normally non-conductiveduring times long compared to theduration -of the pulseinthe trip-outputcircuit. Because of the suddenness of the operation, the t'hyratronor otheritub'e' M0 becomesefiective with corresponding suddenness to render the lamp- 2 suddenlyiconductive.

:In the tripcircuits *of-each of Figs. 1 and 2,'an energizing 'pulse isdmpres-sed suddenly upon the primary Winding -36 of the transformer 3ll'-by'a discharging surge of :current' from the source of energy constituted of the small second condenser -28. A corresponding sudden energizing pulse may equally well be produced --in the primary -winding36 byacharging surge of currenhduring the chargingof the small condenser 28', however, as occurs in-the'trip circuit-of Fig. 3. In this :case;-the pulse is produced suddenly from the-battery HM or'the before'mentioned =by-pass-condenser, notshown; =In the-trip circuits-of each of Figs. 1, 2 and 3, the control electrode :loses 'control over the thyratron J40 upon the initiation byethecondenser-flrof thesudden'current impulse -In the trip-circuit -of Fig. 2, when the tube \is rendered conductive, in' response to a voltage .-pulse upon the control grid :50, .irom the-transintermittently upon the thyratron control grid '75 eformerifi l,theipotentialiofthecathode' lil isrraised D c mber 5. 193 reissued as L tt rs 22123. .Tune 23. 1947 and L t rs Pat nt 22.260.

ilo-nearly that of the anode 52. This resultsin I acharging surge of current into the small second course, be brought about in other ways also, as

by the use of electrical-transients in transformers, or by impulses from photo-electric cells, amplifiers, etc. In the trip circuit of Fig. 5, as a further example, the signal for controlling the flashes of light is supplied to the grid 50 through the closing of a switch contactor 32. Upon the closing of the switch contactor 32, at any time after the condenser 28 has become charged, the grid 5!! of the thyratron I40 will receive a, potential stimulus of the same nature as already described, to effect the discharge of the small second condenser 28 into the primary winding 36.

The input circuit of the trip circuit or the input or grid circuit of the thyratron I40 of Fig. 5 may be traced from the cathode 48, through various impedances, shown as resistors, a portion of the impedance 33, and an impedance I42, also shown as resistors, to the control-grid electrode 50. The tripping is performed by a control series circuit between the control grid 50 and the anode 52. In this control series circuit. the control grid 5!! is shown connected to one side of the switch 32 through a trio condenser 59. which may be as small as 0.00025 microfarad, in parallel with a leak resistor I43. The other side of the switch 32 is connected to the anode 52 through the primary winding 36. The control grid 50 is connected also to a negatively biased portion of the resistor 33, in series with the resistor M2,. The resistance of the resistor I42 limits any current that may tend to flow when the grid 50 becomes positive. or when there is any ionization in the tube. Especially in variable-s eed stroboscopes, the adju tment of a. suitable impedance. such as the impedance I9 of Fig. 3. may be employed to var the intensity of the startin voltage applied to the start ng-grid electrode I00.

The output circuit of the trip circuit or of the th ratron I 40 of F g. 5 maybe traced from the ca hode 8. throu h an imp dance. shown a resistor. the small conden er 28 and the primary wi in 3 to he anode 2.

In the tr o circu s of Fig. 5, the closing of the switch contactor 32 may be contro led in any de re manner. manually or automatic l y. An example of an automatic control. eflec ed throu h. the medi m of a p riod ally rnnv hle, member. is de cr bed in Tetters Patent 2.18 .879, issu d Pa nt Feb uar 2. .1943. The sw tch 32 ma be very sm ll. since it need c rry onl ver sm l currents.

The nvention of the said application. Serial No. 5 501. ther fore. makes it poss ble to operate the s stem with ut any switches or other movin parts. exce t. in some cases. as with the aid of the very small sw tch contactor 32. for causin the th ratron or other gas-discharge tube I 40 to funct on.

By varying the fre uency of the oscillator 62 or the speed of o eration of the switch 32 of he illustrated trip circuits, it is possible to vary the number of times per second'th t the external si nal is appliedto the control grid 50 to control rate at which the signal is applied may thus be varied to vary the selected intervals of flashing.

The rate of flashing may be controlled, how ever. by suitably varying the frequency in other ays also. The voltage-impulse stimulus may, for example, be transmitted from the control circuit to the output circuit of the trip circuit, and from this output circuit to the lamp 2, to produce the flashes of light, without any outside aid, such as the oscillator 62 of Fig. 2 or the switch contactorof Fig. 5, purely through self-oscillation of the system. The tripping surges in the grid circuit may be supplied by transformer or capacity coupling as commonly used in the art, or in any other desired manner.

The control may, for example, be efiected by varying the impedance 3! or 33, as for example, by connecting the control grid 50 to various taps on the resistance 33 or 3|, as illustrated at I 46 in Fig. 1, and at I49, in Fig. 3, and also in Figs. 4, 5 and 6, to cause the thyratron I40 to oscillate as a relaxation oscillator.

The adjustment of either tap may thus control the flashing rate of the condenser 28 and, therefore, the frequency of the high-voltage surges that become impressed upon the starting electrode N10.

The impedances 3! and 33 need not, however, be resistive. If. for example, the impedance 3I is reactive, or if there are other circuit conditions such that the voltage of the grid 5!! may exceed the critical starting potential. the thyratron circuit may, under certain conditions, generate its own oscillations at a frequency determined by the circuit constants and the characteristics of the tube Hill. The thyratron or other gaseous-discharge device E40 will under these circumstances also oscillate as a. self-excited relaxation oscillator. The electrical impulses for stimulating the thyratron control grid 50 in order to initiate the discharges of the condenser 26 through the lamp 2 at the desired selected intervals may thus be produced at a controlled rate determined by the adjustment of this self-excited relaxation oscillator.

The self -excited relaxation-oscillator thyratron. circuit described in the preceding paragraphs as initiating discharge of the condenser 26 at selected intervals is sometimes termed a self-excited static inverter. This inverter produces electrical impulses at a controlled rate determined by its adjustment. If an external. signal is used to trip the thyratron (such as from the rid transformer 64 and the oscillator 62 illustrated in Fig. 2). the circuit is sometimes called a driven static inverter.

The manner of connecting the grid for selioscillation depends upon the characteristics of the particular thyratron that is used. For thyratrons with a negative control characteristic (which start when the grid voltage is negative). circuits of the type shown in Figs. 2, 3. 5 and 6 may be used. For thyratrons with a positive control characteristic (which start when the grid voltage is positive) circuits of the types shown in Figs. 1, 5 and 6 may be used. Thyratrons, furthermore, especially the inverter types that have a short deionization time, require a certain amount of grid current in order to conduct. Often a positive voltage is required on the grid of a negative-control thyratron to supply the required grid current through the grid resistor M2. The grid resistor I42, if varied, will vary the selfoscillation rate, if grid currents are necessary for starting.

annaooe fiche 'fl-a'shes' off-light tromthe tube-anemont'rolled by' the oscil lationssof the inverter, and adjustment of the irequency. may he made by changing the value voi th'e charging resistance.

The itli-yratron does not conduct {current when there are no impulses in the grid circuit, except "when used' f'or self-oscillation,as described. The roscillator .62, '%the switch l filand the self-excited oscillations are :alternatire arrangements, all 'iu'l-ly equivalent for the purpose of wroducing the above-described stimulus upon the thyratron oo-ntrol grid 513 for causing the discharge ofrithe slash condenser 26 ithrough the lamp 2. In all cases, the :light flashes will :occur accurately and reliably, at just the desired selected intervals, in response "to the discharge of the condenser is through t. eitube 'once during each-cycle of the oscillations =-ofthe oscillatoriez, or of the selfoscillations, or once-corrcsponding to each closing :of the very small switch montactor 32. :cases, the voltage impulses will' thus occur at the instant that the current now through the tube tllfl :is conveyed, through the transformer t the flash-producing .apparatus.

The electrical narameters of the discharging circuit of the condenser 25 are such that, if the 1-2 wereaconductive :inlb oth. directions between cipal 1 electrodes 4 land ifi,'the :c'ircuit "would z'ee oscillatory. @ILhis :osciklatory tendency is "use- :fiul, however, since it :assists in .nreventin :tinuous ftow 10f recurrent through the lam i-t-he directcurrent power supply, :such :as h attery M2. The ac'ond'enser Z5 is charged with potential of an'opposit'e polarity after a surge of :eurrent flows through it'he tube 2; voltage .:is tl'm's put ecnflihe to de onize the tube.

tithe thyratron MO is :a mecti'fienthe current "in the circuit comprising the condenser 28 "and 'lthe'stransformer :39 :cannot :oscillate, although there is'ra tendency to do :so.

"The resistance 3 *may be'made to have a' high value; 'or"it:maylbe:open dircuitedfiif self-oscillations are desired. Variation o'fthe tap 146 on the resistor (Fig. "1 or other variation of thevalue of the resistor 33, will vary the frequency of the self-excited static inverter circuit justdescribed. Avaria'ble impedance 3'3, included-as an element in "the inverter circuit (Fig. 3-), may be connected with the tube 140 in the charging ciredit of "the second condenser 28 for varying the impulse :rate 'by. controlling the current flowing through the tube I'M and,therefore the intervals between condenser discharges. Similar remarks apply to variation oflthe 'tap 1149 of the resistor 33 of Fig. 3.

The grid -50 in this vcase,.sho wn connected, through the .resistor 1.42,, to the tap 1.4.9 of, the resistor .33, connected in parallel to the condenser '28, thus providing a variableimpedance shunted across the second-condenser 28. In Figs. 1 and 2, .onthe other .hand, as previously stated, the sec- .ond condenser 2-8 .is shown shunted across the lmain electrodes dfiand .52\of the -g-aseous-dis-; .-charge device 149. In all cases, the condenser -28 i-iS causedito discharge through the gaseousconductor device I40 by varying the potential of the -.grid electrode -50.

"anode which helps :Eigs. v.4, .5 and -6 illustrate circuits that are efiinient :ior charginguthe discharge condenser 2.6. .In .Fligs; Land 5, the charging circuit consists of the impedance .35 :in series with :a rectifier tube, .shown :at Tin Fig; 4 .and iat TIM in Fig. :5. The tubes fl iand ilzllfliftlash as they charge the con- In all A. negative 14 d'enser 1Z6 sand arsecond fiash is obtained whlm asecondt-tube' zsshortecircuits the nondenser :25;

.Acircuit breaker il -29 (Rig. .4). :isvuseful rfor protection :of high-effici'ency charging circuits-,since :largeacurrentssare apt to down the tube 2 does :not operate properly. The iholdover .current through fthe tube :2 :is' limited by "the -regulation of the power supply 'lfll2, the resistance :of iimipeda'nce 3.5, and the effective resistance .of the tube 2.

.The operation of .the remainder :of the-circuit .of Fig. '4;is the-sameza's Jhasbeennescribedin the discussion of Fig. .2, .except that the :grid :of-Ethe tube Z7 is shown connected :to the cathode. thyratron I48 forms an inverter of the self-driven 1type-in :contuncti'on "with .the other component spartscof :the circ1iit; The flashes of light'i'from the tube 2 are controlled byitheoscillationo'f l the sinverter,and-adjustment of the .frequ'encyais snade by changing :the value .of :the .charging resistance 33.1.

In Fig. 5, thereotifierltube illll,zas:beforelstated, is illustrated as of the same typesasithe flash tube 2. Control is obtained :byra surge-into the trans- "iorm'er 538a irom a athyratron inverter, :eit'hersen -:oscilla'tory or externally driven, :as has ibeenrdescribed in connection .withithe Figs. 71, 2 and :3.

Fig. 56 illustrates acircuit arrangement that n's :particularly useful for obtaining flashes .of light that :are multiples of the line frequency.

"The anode of a further thermionicxor :gaseousdischarge half-wave rectifier tube 21 is connected toa tap tea 7 of the transformer ssecondary 'winding I41. Thexcathode of thefurther re'ctifierzl is connected in series with .an adjustable imsp'edance 31, shown as :a resistor, to charge' the second-condenserfia. The connection :of lth'e condenser 28 to the cathode of the rectifier 2! through the resistor 131 :is similar :to that :of thecathode :1 of the rectifier .-2ll sthroughith'e impedanceabsto the condenser 26. Thelirectifier 2l charges :the-: condenser 12:8 irom xthe same alternating source 2M4 of voltage :as the condenser .26, but through the impedance :31.

The cathode iDf the rectifier 21! :shown :cxm-

nected :also through :the impedance .3ll shonmns a resistor, to the anode 52 of the .thyratron 1M0, similarly to the -:connection of the cathode .ofthe rectifieritito the :anode 16 of :the lamp .2. The gridfili. of the .thyratronjffl is connected through the resistor 142150 that :end of :thefurthensec- .rondary winding :lGfi .of' the transformer :HlB that zis negative'tduring thejhalf-cycle while the connenserszznzanii 1-28 are being rcharged.

' While the grid i'o'lliis negative, theitlnnatronfis zinefiectirreiand, therefore, the condensers :28 and 26 are permitted to accumulate a charge. Qnzthe succeeding halicycle, the grid kill swings :positive and theithyratron .l-lEl which, in turmcauses the'zrnain condenserzfit to discharge through the .cnercur-yearc tube .2, :as has been :preyionsly explained;

The: nanlable mesistance .31 "or M2 makes .it zpos- :sibleto arrange the =circuit so that .flashes :every eothert'cycle or every third cycle or other sub- :the :primary winding 36., :by way of the conductor 8, through the portion it!) of the secondary Windting-I47, :and amvimpedance M2,, shown lasniresistor, toiiihercmitrolegridseledtmdefll; .l-Ilhe the intermediate portion of the secondary wind- ,ing I41 into direct current for this output circuit.

The circuit of Fig. 6 constitutes the subject matter of a divisional application, Serial No. 688,405, filed August 5, 1946.

Further modifications will occur to persons skilled in the art, and all such are considered to fall within the spirit and scope of the invention,

,as defined in the appended claims.

What is claimed is:

1. In combination with apparatus for producing electrical-energy flashes of the type in which a condenser is periodically discharged through a gaseous-conductor lamp, means for initiating discharge of the condenser at selected intervals consisting of a relaxation oscillator for producing electrical impulses at a controlled rate, said relaxation oscillator comprising a gaseous-discharge device connected in circuit with a source of potential and with means for varying the impulse rate comprising a variable impedance, means for conveying such impulses to the flashproducing apparatus, and means for adjusting the quantity of light in the electrical-energy flashes.

2. Light-flashing apparatus having, in combination, a light-flashing tube, a condenser connected to the tube to discharge through the tube to produce a flash of light, means for connecting the condenser to a source of energy, capacitive means in series with the condenser and the tube, and means for adjusting the capacitive means i to adjust the quantity of light contained in the flash of light.

3. Light-flashing apparatus having, in combination, a light-flashing tube, a condenser connected to the tube to discharge through the tubeto produce a flash of light, means for connecting the condenser to a source of energy, transformer means separate from the source of energy in series with the condenser and the tube and means for adjusting the transformer means to adjust the quantity of light contained in the flash of light.

4. In combination with apparatus for producing electrical-energy flashes of light of the type in which a condenser is periodically discharged through a gaseous-conductor lamp, means for init'ating discharge of the condenser at selected intervals consisting of a relaxation oscillator for producing electrical impulses at a controlled rate, said relaxation oscillator comprising a gaseousdischarge device in series circuit with a source of potential and with a second condenser, means for varying the impulse rate comprising a variable impedance shunted across said second condenser, means for conveying such impulses to the flashproducing apparatus, and means for adjusting the quantity of light contained in the flashes of light.

5. In combination with apparatus for producing electrical-energy flashes of the type in which a condenser is periodically discharged through a gaseous-conductor lamp, means for initiating discharge of the condenser at selected intervals consisting of a relaxation oscillator for producing electrical impulses at a controlled rate, said relaxation oscillator comprising a gaseous-discharge device connected in circuit with a source of potential, a second condenser shunted across the gaseous-discharge device, means for varying the impulse rate comprising a variable impedance connected in the charging circuit of the second condenser, means for conveying such impulses to the flash-producing apparatus, and means for adjusting the quantity of light in the electricalenergy flashes.

6. In combination with apparatus for producing electrical-energy light flashes of the type in which a condenser is periodically discharged through a gaseous-conductor lamp, means for initiating discharge of the condenser at selected intervals comprising a discharge device connected in circuit with a source of potential and with means for varying the impulse rate, means for conveying such impulses to the flash-producing apparatus, and means for adjusting the quantity of light in the light flashes.

7. In combination with apparatus for producing electrical-energy light flashes of the type in which a condenser is periodically discharged through a gaseous-conductor lamp, means for initiating discharge of the condenser at selected intervals comprising a gaseous-discharge device connected in circuit with a source of potential, a second condenser shunted across the gaseousdischarge device, means for varying the impulse rate, means for conveying such impulses to the flash-producing apparatus, and means for adjusting the quantity of light in the light flashes.

8. A stroboscope having, in combination, a normally non conductive gaseous conductor lamp for producing light flashes of substantial illumination intensity having two electrodes, means for connecting the electrodes to a source of energy to impress between the electrodes from the source a voltage of magnitude insuflicient to produce a current impulse from the source through the lamp between the electrodes when the lamp is non-conductive but sufficient to produce a current impulse from the source through the lamp between the electrodes to produce a light flash when the lamp is conductive, a trip circuit comprising a discharge device, means for connecting the discharge device to the lamp, means for impressing impulses at a predetermined rate upon the discharge device, means controlled by the discharge device in response to the impulses for producing sudden violent electrical transient impulses at the predetermined rate, and means for transmitted the transient impulses to the lamp to render the lamp suddenly conductive at selected intervals in accordance with the predetermined rate in order to produce current impulses from the source through the lamp between the electrodes at the selected intervals to produce light flashes of substantial illumination intensity at the selected intervals, and means for adjusting the quantity of light in the light flashes.

9, A stroboscope having, in combination, a normally non conductive gaseous conductor lamp for producing light flashes of substantial illumination intensity having two electrodes, means for connecting the electrodes to a source of energy to impress between the electrodes from the source a voltage of magnitude insufficient to produce a current impulse: from the source through the lamp between the electrodes when the lamp is non-conductive but suiflcient topro: duce a current impulse from the source through the lamp between the electrodes to produce a light flash when the lamp is conductive, a trip circuit com-prising a condenser, means for charging the condenser, a. discharge device connected between the condenser and the lamp, means for impressing impulses at a predetermined rate upon the discharge device, and means controlled by the discharge device in response to the impulses for causing the condenser to produce sudden violent electrical transient impulses at the predetermined rate for transmission through the discharge device tothe lampto render the lamp suddenly conductive at selected intervals in accordance with the predetermined rate in order to produce current impulses from the source through the lamp between the electrodes at the selected intervals to produce light flashes of substantial illumination intensity at the select-ed intervals, and means for adjusting the quantity of light in the light flashes.

10. A stroboscope having in combination, a normally non conductive gaseous conductor lamp for producing'light flashes of substantial illumination intensity having two electrodes, means for connecting the electrodes to a first source of energy to impress between the elec-' trodes from the source a voltage of magnitude insuflicient to produce a current impulse from the source through the lamp'between the electrodes when the lamp is non-conductive but suiflcient to produce a current impulsefromv the source through the lampbetween the electrodes to produce a light flash whenthe lamp is conductive, a trip circuit comprising a discharge device having two principal electrodes and a control electrode, an output circuit connected to the principal electrodes provided with a second source of energy, means for normally maintaining the control electrode at a predetermined potential to maintain the discharge device normally non-conductive, means for modifying the predetermined potential at a predetermined rate to render the discharge device conductive at the predetermined rate in order that the second source of energy may produce suddent Violent electrical transient impulses in the output circuit at the predetermined rate, means whereby the normally maintaining means maintains the control electrode at the predetermined potential.

during times long compared to the duration of the transient impulses inthe output circuit, and means for connecting the output circuit to the lamp to transmit the transient impulses to the lamp to render the lamp suddenly conductive at selected intervals in accordance with the predetermined rate in order to produce current. impulses from the firstsource through the lamp between the electrodes at the selected intervals to produce light flashes of substantial illuminawhen therlamp is non-conductive-but suflicient to effect a discharge; of the first condenser through the lamp between. the electrodes to produce a light flash whenthe lamp is conductive, atrip'circuit comprising, a second condenser, means for charging the second condensena dis.- charge device connected between the second-con,- denser and the lamp, means for'irnpressing impulses at a predetermined rate upon the discharge device, and means controlled by the discharge device in-response to the impulses for causing the secondcondenser to induce sudden violent electrical transient impulses at the predetermined rate for transmission through the discharge device to the lamp. to render the lamp suddenly conductive at selected intervals in accordance with the" predetermined rate in order to effect discharges of the first condenser through the lampbetween the electrodes at the selected intervals to produce light flashes of substantial illumination. intensity at the selected intervals,and means for adjusting the quantity of light in thelight flashes.

12, A light-flash producer having, in combination, a normally non-conductive gaseous-conductor lamp for producing light flashes of substantial illumination intensity having two electrodes, means for connecting the electrodes to a source ofienergy toimpress between the electrodes from the source of voltage of magnitude insuflicient to produce a current impulse from the source through the lamp-between the electrodes when the lamp is non-conductive but sufficient to produce a current impulse from thesource through the lamp between the electrodesto pro. duce a light flash when-thelarnp 'isconductive, a trip circuit comprising a normally non-conductive discharge'device, means for connecting the discharge'deviceto the lamp, means for impressing an impulse upon the discharge device to render the discharge device conductive, means controlled by the discharge device upon the discharge device becoming conductive ior producing a sudden violent electricaltransient impulse, and means for transmittingthe transient impulse to the lamp: to render the lamp-suddenly conductive in. order to produce a current impulse from the. source'through the, lamp between the electrodes to produce a. light flash of substantial illumination intensity, and means for adjusting the quantityof light'int'he light flash;

13.- A light-flash producer-havingin combination, anormally non-conductive gaseous-conductor lamp for producing light flashes of substantial illumination. intensity having two electrodes, means for connectingthe electrodes to a first source r energy to impress between the electrodes fromrthe sourceia voltage of magnitude insufficientnto produce a current impulsefrom the source through the lamp between. the 818C? trodes when the lamp is non-conductive but sutficientto: produce a current impulse from the sourcethroughthe lamp between the electrodes tov producealight flash when thelamp is conductive, a trip circuit-comprising a discharge device having. two. principal electrodes, and a con: trol electrode, an output circuit connected to the principal electrodes; provided with a condenser and a secondscurce, of energy for charging the condenser, .a transformer havinga, primary; Wind-' ing connected in the output circuit and a secondary winding, means for normally maintaining the control electrode at a predetermined potential to maintain the discharge device normally non-conductive, means for modifying the predetermined potential to render the discharge device conductive in order that the condenser may produce a sudden current impulse in the output circuit to impress a sudden violent electrical transient impulse upon the primary winding, means-whereby the normally maintaining means maintains the control electrode at the predetermined potential during a time long compared to the duration of the transient impulse, and means for connecting the secondary winding to the lamp to transmit the transient impulse in the primary winding through the secondary winding to the lamp to render the lamp suddenly conductive in order to produce a current impulse from the first source through the lamp between the electrodes to produce a light flash of substantial illumination intensity, and means for adjusting the quantity of light in the light flash.

' ,,14. A light-flash producer having, in combination, a normally non-conductive gaseous-conductor lamp for producing light flashes of substantial illumination intensity having two electrodes, means for connecting the electrodes to a first source of energy to impress between the electrodes from the source a voltage of magnitude insufficient to produce a current impulse from the source through the lamp between the electrodes when the lamp is non-conductive but sufficient to produce a current impulse from the source through the lamp between the electrodes to produce a light flash when the lamp is conductive, a trip circuit comprising a gaseousdischarge device having two principal electrodes and a control electrode, an output circuit connected to the principal electrodes provided with a condenser and a second source of energy for charging the condenser, means for normally maintaining the control electrode at a predetermined potential to maintain the discharge device normally non-conductive, means for modifying the predetermined potential to render the discharge device conductive in order that the condenser may produce a sudden violent electrical transient impulse in the output circuit, means whereby the normally maintainin means maintains the control electrode at the predetermined potential during a time long compared to the duration of the transient impulse, and means for connecting the output circuit to the lamp to transmit the transient impulse to the lamp to render the lamp suddenly conductive in order to produce a current impulse from the first source through the lamp between the electrodes of the lamp to produce a light flash of substantial illumination intensity, the gas pressure of the discharge device being such that the control electrode loses control over the discharge device upon the initiation of the production by the condenser of the sudden current impulse in the output circuit, and means for adjusting the quantity of light in the light flash.

15. A light-flash producer having, in combination, a normally non-conductive gaseous-conductor lamp for producing light flashes of substantial illumination intensity having two electrodes, a condenser, means for connecting the condenser to the electrodes, means for charging the condenser to a voltage of magnitude insufficient to effect a discharge of the condenser through the lamp between the electrodes when the lamp is non-conductive but'sufflcient to effect a dis charge of the condenser through the lamp between the electrodes to produce alight flash when the lamp is conductive, a trip circuit comprising a discharge device, means for connecting the discharge device to the lamp, means for impressing an impulse upon the discharge device, means controlled by the discharge device in response to the impulse for producing a sudden violent electrical transient impulse, and means for transmitting the transient impulse to the lamp to render the lamp suddenly conductive in order to effect a discharge of the condenser through the lamp between the electrodes to produce a light flash of substantial illumination intensity, and means for adjusting the quantity of light in the light flash.

16. A light-flash producer having, in combination, a normally non-conductive gaseous-conductor lamp for producing light flashes of substantial illumination intensity having two electrodes, a first condenser, means for connecting the first condenser to the electrodes, means for charging the first condenser to a voltage of magnitude insuflicient to efiect a discharge of the first condenser through the lamp between the electrodes when the lamp is non-conductive but sumcient to effect a discharge of the first condenser through the lamp between the electrodes to produce a light flash when the lamp is conductive, a trip circuit comprising a second condenser, means for charging the second condenser, a discharge device connected between the second condenser and the lamp, means for impressing an impulse upon the discharge device, and means controlled by the discharge device in response to the impulse for causing the second condenser to produce a sudden violent electrical transient impulse for transmission through the discharge device to the lamp to render the lamp suddenly conductive in order to effect a discharge of the first condenser through the lamp between the electrodes to produce a light flash of substantial illumination intensity, and means for adjusting the quantity of light in the light flash.

HAROLD E. EDGERTON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS OTHER REFERENCES ,Hot Cathode Thyratrons" by A. W. Hull, paper #491, pp. 3-23.

Reprint from G. E. Review (pp. 213-223, Apr. 1929, and pp 390-399 of the July issue) Certificate of Correction Patent No. 2,478,904 August 16, 1949 HAROLD E. EDGERTON It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows:

Column 16, line 59, for the word transmitted read transmitting;

and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Oflice. Signed and sealed this 21st day of March, A. D. 1950.

THOMAS F. MURPHY,

Assistant Oommz'ssioner of Patents. 

